1. Field of the Invention
The present invention relates to the preparation of POY (partially oriented yarn) of increased birefringence and orientation at a given wind-up speed. More particularly, the present invention relates to the preparation of partially oriented polyester yarn of increased birefringence for a given wind-up speed by passing extruded polyester filamentary material through a hot zone subsequent to a quenching of the material but with the filamentary material still being in a deformable state.
2. Description of the Prior Art
In conventional filament spinning processes, for example, in the spinning of polyester yarn, the orientation of the spun filamentary material, as measured by birefringence, increases with increased wind-up speeds. Process parameters such as the spinning temperature and quench flow can be adjusted accordingly to increase the birefringence at a constant or given wind-up speed, however, the effects are generally minor and/or the process changes result in much poorer yarn uniformity.
The use of a hot tube or hot zone in spinning processes are known to achieve various effects. For example, melt spinning processes have been proposed wherein the cooling of the extruded filamentary material has been retarded, i.e., prolonged, prior to solidification so as to alter the properties thereof. See, for instance, U.S. Pat. No. 2,323,383; and 3,361,859. Such processes generally pertain to the use of a hot shroud immediately below the spinneret face so as to maintain the extruded filaments in a molten state for a predetermined period of time.
U.S. Pat. No. 3,053,611 pertains to a process for spinning fully stretched fibers by fully stretching the fibers upon leaving the spinning jet, whereby they are spun in a spinning shaft whose upper part is heated to 10.degree.-80.degree. C. below the melting point of the resin to be spun and whose lower part is heated to a temperature below 100.degree. C.
U.S. Pat. No. 3,969,462 discloses a method for the production of an industrial polyester filament yarn wherein a plurality of filaments are melt-spun into a heated zone coupled with controlled cooling. In particular, the process disclosed produces yarn by melt spinning into a heated zone which maintains the filaments molten for an interval below the spinneret face with subsequent quenching of the filaments being achieved with a radial outflow of cooling gases, thereby producing a low birefringence yarn which is capable of being drawn at high draw ratios to high tenacities.
U.S. Pat. No. 3,946,100, of common assignee, discloses a process for producing polymeric filamentary material or film of improved tensile strength and modulus and diminished shrinkage characteristics, wherein a thermal conditioning zone is employed after solidification of the melt spun filamentary material, but prior to wind-up. In the process, molten meltspinnable polymeric material capable of undergoing crystallization, such as a polyester, is extruded through a shaped orifice to form a filamentary material or film, quenched to below its glass transition temperature to form a solid filamentary material or film, and then passed for a brief residence time through a thermal conditioning zone at a temperature between its glass transition temperature and its melting temperature wherein substantial crystallization of the previously solidified filamentary material takes place under high stress conditions. The filamentary material is then withdrawn from the thermal conditioning zone. Thereby, the birefringence and tensile properties of the filamentary material are increased and improved so much so that a conventional hot drawing step may be unnecessary. U.S. Pat. No. 4,195,161, also a common assignee, more fully describes the unique polyester fiber which is obtained thereby.
See also European Application No. 0,034,880 and the patents discussed therein regarding melt spinning processes employing a thermal conditioning zone provided with a gaseous atmosphere at a temperature above the glass transition temperature of the filamentary material but below its melting temperature, through which a solidified filamentary material is passed prior to wind-up.
It is an object of the present invention, however, to provide an expeditious and improved process for achieving partially oriented yarn products exhibiting POY like properties but exhibiting significantly higher orientation for a given or constant wind-up speed.
It is another object of the present invention to provide a process for achieving high wind-up speed orientation in a partially oriented yarn at lower wind-up speeds via the use of a hot zone.
It is still another object of the present invention to provide an expeditious process for preparing partially oriented polyester yarn which is subsequently to be drawn and/or textured.
These and other objects, as well as the scope, nature and utilization of the invention, will be apparent to those skilled in the art from the following description and appended claims.